Thanks to an article by Skippy, and considerable time staring at Postfix, The Definitive Guide, I’ve gotten a whitelisting system set up for my daughter. She can now receive email from a very select list of addresses. Anyone else gets rejected.
The second part is to get a whitelisting proxy server set up for her.
And, no, I’m not interested in your remarks about how overprotective I am, or how I’m stunting her ability to learn, so don’t even bother.